Golf ball

ABSTRACT

In a golf ball having a rubber core of at least one layer and a cover of at least one layer encasing the core, at least one layer of the cover is formed of a resin composition that includes (A) polyurethane or polyurea, and (B) a thermoplastic polyester elastomer. Component (B) is included in a ratio of not more than 45 wt % of the overall amount of the resin composition, and the resin composition has a Shore D hardness of 42 or less and a rebound resilience of from 60 to 72%. The golf ball has an excellent controllability on approach shots, is able to maintain a good feel at impact and a good scuff resistance, and also has a good moldability.

CROSS-REFERENCE TO RELATED APPLICATION

This non-provisional application claims priority under 35 U.S.C. §119(a) on Patent Application No. 2020-096539 filed in Japan on Jun. 3,2020, the entire contents of which are hereby incorporated by reference.

TECHNICAL FIELD

This invention relates to a golf ball which has a core of at least onelayer and a cover of at least one layer.

BACKGROUND ART

The chief property desired in a golf ball is an increased distance, butother desirable properties include the ability for the ball to stop wellon approach shots and a good scuff resistance. Many golf balls thatexhibit a good flight performance on shots with a driver and aresuitably receptive to backspin on approach shots have hitherto beendeveloped. Recently, an increasing number of golf balls for professionalgolfers and skilled amateurs use urethane resin materials in place ofionomer resin materials. Thermoplastic urethane elastomers in particularare often used as the urethane resin material, and their properties areconstantly being upgraded. A number of disclosures have been made thatfurther improve the properties of cover resin compositions in which athermoplastic urethane elastomer serves as the base resin by includingother resins and additives.

However, there is a desire, when blending a thermoplastic urethaneelastomer with another resin material, to keep the scuff resistanceinherent to the thermoplastic urethane elastomer from decreasing bysuitably adjusting the type and amount of that resin. In addition, thereis also a desire, when blending a urethane resin material with anotherresin material for the purpose of lowering the hardness, to avoid asmuch as possible a change in the resilience and a worsening of themoldability.

For example, JP-A 2008-119461 describes the use of a low-hardnessurethane resin as the cover material, although softening of the resinmaterial is required to further enhance the spin rate on approach shots.In this case, further softening the urethane resin-based cover materialitself worsens the moldability, making production difficult at thispoint in time. Hence, the notion of including additives so as to softenthe cover material is also described.

In this connection, JP-A 2017-12737 and other art describes golf ballsin which the resin composition is softened by including a plasticizerwithin a urethane-based resin composition. However, the resincomposition in this case merely becomes softer and fails to adequatelyenhance the spin rate on approach shots.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a golfball which has an excellent controllability on approach shots and whichalso can maintain a good feel at impact and a good scuff resistance andmoreover has a good moldability.

With this object in mind, in order to further improve a resin materialcomposed primarily of polyurethane or polyurea as the cover material ina golf ball having a core and a cover, I began by weighing (i) theaddition of a plasticizer versus (ii) the addition of a resin havingsoftening properties. As a result, I learned that, with the firstapproach, i.e., (i) plasticizer addition, the resin composition merelybecomes softer and, in the molded ball, is unable to increase the spinrate of the ball on approach shots. Also, I realized from theexperimental results for (i) that, in order to achieve the object ofthis invention, the material that is added must have a certainresilience. I then selected a resin that has softening properties forthe second approach (ii) and fabricated a golf ball using as the coverthe molded form of a resin composition obtained by including a specificamount of a specific, relatively soft, thermoplastic polyester elastomerin a polyurethane or polyurea-based resin composition, whereupon Idiscovered that this golf ball has an excellent controllability onapproach shots, is able to maintain a good feel at impact and a goodscuff resistance, and moreover has a good moldability. This inventionwas thus arrived at based on the finding that, in a resin compositioncontaining polyurethane or polyurea as the base resin ingredient, thespecific thermoplastic polyester elastomer, when used as the addedresin, has a good compatibility with the polyurethane or other baseresin, gives the resin composition a low hardness, imparts at least acertain degree of resilience and has hardenability.

Accordingly, the present invention provides a golf ball having a rubbercore of at least one layer and a cover of at least one layer encasingthe core, wherein at least one layer of the cover is formed of a resincomposition containing (A) polyurethane or polyurea and (B) athermoplastic polyester elastomer, component (B) being included in aratio of not more than 45 wt % of the overall amount of the resincomposition and the resin composition having a Shore D hardness of 42 orless and a rebound resilience of from 60 to 72%.

In a preferred embodiment of the golf ball of the invention, the reboundresilience of the resin composition is from 62 to 70%.

In another preferred embodiment, the polyurethane or polyurea serving ascomponent (A) has a Shore D hardness of 45 or less and a reboundresilience of at least 55%.

In yet another preferred embodiment, the thermoplastic polyesterelastomer serving as component (B) has a Shore D hardness of not morethan 35 and a rebound resilience of at least 65%.

In still another preferred embodiment, component (B) has a meltviscosity at 200° C. and a shear rate of 243 sec⁻¹ which is from 0.2×10⁴to 1.0×10⁴ dPa·s.

Advantageous Effects of the Invention

The golf ball of the invention has an excellent controllability onapproach shots, is able to maintain a good feel at impact and a goodscuff resistance, and moreover has a good moldability.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The objects, features and advantages of the invention will become moreapparent from the following detailed description.

The golf ball of the invention is a ball having a core of at least onelayer, which core is encased by a cover of at least one layer; that is,a single-layer cover or a multilayer cover.

The core may be formed using a known rubber material as the basematerial. A known base rubber such as natural rubber or a syntheticrubber may be used as the base rubber. More specifically, it isrecommended that polybutadiene, especially cis-1,4-polybutadiene havinga cis structure content of at least 40%, be chiefly used. If desired,natural rubber, polyisoprene rubber, styrene-butadiene rubber or thelike may be used together with the foregoing polybutadiene in the baserubber.

The polybutadiene may be synthesized with a metal catalyst, such as aneodymium or other rare-earth catalyst, a cobalt catalyst or a nickelcatalyst.

Co-crosslinking agents such as unsaturated carboxylic acids and metalsalts thereof, inorganic fillers such as zinc oxide, barium sulfate andcalcium carbonate, and organic peroxides such as dicumyl peroxide and1,1-bis(t-butylperoxy)cyclohexane may be included in the base rubber. Ifnecessary, commercial antioxidants and the like may be suitably added.

The core may be produced by vulcanizing/curing the rubber compositioncontaining the above ingredients. For example, production may be carriedout by kneading the composition using a mixer such as a Banbury mixer ora roll mill, compression molding or injection molding the kneadedcomposition using a core mold, and curing the molded body by suitablyheating it at a temperature sufficient for the organic peroxide and theco-crosslinking agent to act, i.e., from about 100° C. to about 200° C.,and preferably from 140 to 180° C., for a period of 10 to 40 minutes.

In the golf ball of the invention, the core is encased by a single-layeror multilayer cover. This golf ball may be in the form of, for example,a golf ball having a single-layer cover over a core, or a golf ballhaving a core, an intermediate layer encasing the core, and an outermostlayer encasing the intermediate layer.

In this invention, at least one layer of the cover is formed of a resincomposition containing components (A) and (B) below:

(A) polyurethane or polyurea

(B) a thermoplastic polyester elastomer.

(A) Polyurethane or Polyurea

The polyurethane (A-1) or polyurea (A-2) serving as this component isdescribed in detail below.

(A-1) Polyurethane

The polyurethane has a structure which includes soft segments composedof a polymeric polyol (polymeric glycol) that is a long-chain polyol,and hard segments composed of a chain extender and a polyisocyanate.Here, the polymeric polyol serving as a starting material may be anythat has hitherto been used in the art relating to polyurethanematerials, and is not particularly limited. It is exemplified bypolyester polyols, polyether polyols, polycarbonate polyols, polyesterpolycarbonate polyols, polyolefin polyols, conjugated dienepolymer-based polyols, castor oil-based polyols, silicone-based polyolsand vinyl polymer-based polyols. Specific examples of polyester polyolsthat may be used include adipate-type polyols such as polyethyleneadipate glycol, polypropylene adipate glycol, polybutadiene adipateglycol and polyhexamethylene adipate glycol; and lactone-type polyolssuch as polycaprolactone polyol. Examples of polyether polyols includepoly(ethylene glycol), poly(propylene glycol), poly(tetramethyleneglycol) and poly(methyltetramethylene glycol). These polyols may be usedsingly, or two or more may be used in combination.

It is preferable to use a polyether polyol as the above polymericpolyol.

The long-chain polyol has a number-average molecular weight that ispreferably in the range of 1,000 to 5,000. By using a long-chain polyolhaving a number-average molecular weight in this range, golf balls madewith a polyurethane composition that have excellent properties,including a good rebound and good productivity, can be reliablyobtained. The number-average molecular weight of the long-chain polyolis more preferably in the range of 1,500 to 4,000, and even morepreferably in the range of 1,700 to 3,500.

Here and below, “number-average molecular weight” refers to thenumber-average molecular weight calculated based on the hydroxyl valuemeasured in accordance with JIS-K1557.

The chain extender is not particularly limited; any chain extender thathas hitherto been employed in the art relating to polyurethanes may besuitably used. In this invention, low-molecular-weight compounds with amolecular weight of 2,000 or less which have on the molecule two or moreactive hydrogen atoms capable of reacting with isocyanate groups may beused. Of these, preferred use can be made of aliphatic diols having from2 to 12 carbon atoms. Specific examples include 1,4-butylene glycol,1,2-ethylene glycol, 1,3-butanediol, 1,6-hexanediol and2,2-dimethyl-1,3-propanediol. Of these, the use of 1,4-butylene glycolis especially preferred.

Any polyisocyanate hitherto employed in the art relating topolyurethanes may be suitably used without particular limitation as thepolyisocyanate. For example, use can be made of one or more selectedfrom the group consisting of 4,4′-diphenylmethane diisocyanate,2,4-toluene diisocyanate, 2,6-toluene diisocyanate, p-phenylenediisocyanate, xylylene diisocyanate, 1,5-naphthylene diisocyanate,tetramethylxylene diisocyanate, hydrogenated xylylene diisocyanate,dicyclohexylmethane diisocyanate, tetramethylene diisocyanate,hexamethylene diisocyanate, isophorone diisocyanate, norbornenediisocyanate, trimethylhexamethylene diisocyanate,1,4-bis(isocyanatomethyl)cyclohexane and dimer acid diisocyanate.However, depending on the type of isocyanate, crosslinking reactionsduring injection molding may be difficult to control.

The ratio of active hydrogen atoms to isocyanate groups in thepolyurethane-forming reaction may be suitably adjusted within apreferred range. Specifically, in preparing a polyurethane by reactingthe above long-chain polyol, polyisocyanate and chain extender, it ispreferable to use the respective components in proportions such that theamount of isocyanate groups included in the polyisocyanate per mole ofactive hydrogen atoms on the long-chain polyol and the chain extender isfrom 0.95 to 1.05 moles.

The method for preparing the polyurethane is not particularly limited.Preparation using the long-chain polyol, chain extender andpolyisocyanate may be carried out by either a prepolymer process or aone-shot process via a known urethane-forming reaction. Of these, meltpolymerization in the substantial absence of solvent is preferred.Production by continuous melt polymerization using a multiple screwextruder is especially preferred.

It is preferable to use a thermoplastic polyurethane material as thepolyurethane, with an ether-based thermoplastic polyurethane materialbeing especially preferred. The thermoplastic polyurethane material usedmay be a commercial product, illustrative examples of which includethose available under the trade name PANDEX from DIC Covestro Polymer,Ltd., and those available under the trade name RESAMINE fromDainichiseika Color & Chemicals Mfg. Co., Ltd.

(A-2) Polyurea

The polyurea is a resin composition composed primarily of urea linkagesformed by reacting (i) an isocyanate with (ii) an amine-terminatedcompound. This resin composition is described in detail below.

(i) Isocyanate

The isocyanate is not particularly limited. Any isocyanate used in theprior art relating to polyurethanes may be suitably used here. Use maybe made of isocyanates similar to those mentioned above in connectionwith the polyurethane material.

(ii) Amine-Terminated Compound

An amine-terminated compound is a compound having an amino group at theend of the molecular chain. In this invention, the long-chain polyaminesand/or amine curing agents shown below may be used.

A long-chain polyamine is an amine compound which has on the molecule atleast two amino groups capable of reacting with isocyanate groups, andwhich has a number-average molecular weight of from 1,000 to 5,000. Inthis invention, the number-average molecular weight is more preferablyfrom 1,500 to 4,000, and even more preferably from 1,900 to 3,000.Examples of such long-chain polyamines include, but are not limited to,amine-terminated hydrocarbons, amine-terminated polyethers,amine-terminated polyesters, amine-terminated polycarbonates,amine-terminated polycaprolactones, and mixtures thereof. Theselong-chain polyamines may be used singly, or two or more may be used incombination.

An amine curing agent is an amine compound which has on the molecule atleast two amino groups capable of reacting with isocyanate groups andwhich has a number-average molecular weight of less than 1,000. In thisinvention, the number-average molecular weight is more preferably lessthan 800, and even more preferably less than 600. Specific examples ofsuch amine curing agents include, but are not limited to,ethylenediamine, hexamethylenediamine, 1-methyl-2,6-cyclohexyldiamine,tetrahydroxypropylene ethylenediamine, 2,2,4- and2,4,4-trimethyl-1,6-hexanediamine,4,4′-bis(sec-butylamino)dicyclohexylmethane,1,4-bis(sec-butylamino)cyclohexane, 1,2-bis(sec-butylamino)cyclohexane,derivatives of 4,4′-bis(sec-butylamino)dicyclohexylmethane,4,4′-dicyclohexylmethanediamine, 1,4-cyclohexane bis(methylamine),1,3-cyclohexane bis(methylamine), diethylene glycol di(aminopropyl)ether, 2-methylpentamethylenediamine, diaminocyclohexane,diethylenetriamine, triethylenetetramine, tetraethylenepentamine,propylenediamine, 1,3-diaminopropane, dimethylaminopropylamine,diethylaminopropylamine, dipropylenetriamine, imidobis(propylamine),monoethanolamine, diethanolamine, triethanolamine, monoisopropanolamine,diisopropanolamine, isophoronediamine,4,4′-methylenebis(2-chloroaniline), 3,5-dimethylthio-2,4-toluenediamine,3,5-dimethylthio-2,6-toluenediamine, 3,5-diethylthio-2,4-toluenediamine,3,5-diethylthio-2,6-toluenediamine,4,4′-bis(sec-butylamino)diphenylmethane and derivatives thereof,1,4-bis(sec-butylamino)benzene, 1,2-bis(sec-butylamino)benzene,N,N′-dialkylaminodiphenylmethane,N,N,N′,N′-tetrakis(2-hydroxypropyl)ethylenediamine, trimethylene glycoldi-p-aminobenzoate, polytetramethylene oxide di-p-aminobenzoate,4,4′-methylenebis(3-chloro-2,6-diethyleneaniline),4,4′-methylenebis(2,6-diethylaniline), m-phenylenediamine,p-phenylenediamine and mixtures thereof. These amine curing agents maybe used singly or two or more may be used in combination.

(iii) Polyol

Although not an essential ingredient, in addition to above components(i) and (ii), a polyol may also be included in the polyurea. The polyolis not particularly limited, but is preferably one that has hithertobeen used in the art relating to polyurethanes. Specific examplesinclude the long-chain polyols and/or polyol curing agents mentionedbelow.

The long-chain polyol may be any that has hitherto been used in the artrelating to polyurethanes. Examples include, but are not limited to,polyester polyols, polyether polyols, polycarbonate polyols, polyesterpolycarbonate polyols, polyolefin-based polyols, conjugated dienepolymer-based polyols, castor oil-based polyols, silicone-based polyolsand vinyl polymer-based polyols. These long-chain polyols may be usedsingly or two or more may be used in combination.

The long-chain polyol has a number-average molecular weight ofpreferably from 1,000 to 5,000, and more preferably from 1,700 to 3,500.In this average molecular weight range, an even better resilience andproductivity are obtained.

The polyol curing agent is preferably one that has hitherto been used inthe art relating to polyurethanes, but is not subject to any particularlimitation. In this invention, use may be made of a low-molecular-weightcompound having on the molecule at least two active hydrogen atomscapable of reacting with isocyanate groups and having a molecular weightof less than 1,000. Of these, the use of aliphatic diols having from 2to 12 carbon atoms is preferred. Specific examples include 1,4-butyleneglycol, 1,2-ethylene glycol, 1,3-butanediol, 1,6-hexanediol and2,2-dimethyl-1,3-propanediol. The use of 1,4-butylene glycol isespecially preferred. The polyol curing agent has a number-averagemolecular weight of preferably less than 800, and more preferably lessthan 600.

A known method may be used to produce the polyurea. A prepolymerprocess, a one-shot process or some other known method may be suitablyselected for this purpose.

Component (A) has a material hardness on the Shore D hardness scalewhich, to enhance the spin rate on approach shots, is preferably 45 orless, more preferably 44 or less, and even more preferably 43 or less.From the standpoint of the moldability, the lower limit in the materialhardness on the Shore D scale is preferably at least 35, and morepreferably at least 37.

Component (A) has a rebound resilience which, to enhance the spin rateon approach shots, is preferably at least 55%, more preferably at least57%, and even more preferably at least 59%. The rebound resilience ismeasured in accordance with JIS-K 6255: 2013.

(B) Thermoplastic Polyester Elastomer

In this invention, to obtain the desired effects of the invention, aspecific thermoplastic polyester elastomer is included as an essentialingredient in the resin composition. This specific thermoplasticpolyester elastomer imparts at least a certain degree of resilience tothe resin composition and, along with imparting such resilience, enablesthe ball to maintain an elevated spin rate at or above a certain levelon approach shots. Also, because the specific thermoplastic polyesterelastomer included as an essential ingredient in the resin compositionhas a good compatibility with component (A) serving as the base resin,it is able to impart the ball with a good scuff resistance. In addition,including the specific thermoplastic polyester elastomer as an essentialingredient in the resin composition provides the resin composition withat least a certain level of melt viscosity, thus imparting hardenabilityto the resin composition after it has been molded. That is, thethermoplastic polyester elastomer suppresses a decline in the viscosityof the overall resin composition due to the softness of component (A)serving as the base resin, thus preventing a decrease in moldability(productivity) and an increase in appearance defects in the molded golfballs and also holding down a rise in production costs due to anincreased cooling time. This thermoplastic polyester elastomer isdescribed below.

The thermoplastic polyester elastomer serving as component (B) is aresin composition made up of (b-1) a polyester block copolymer and (b-2)a rigid resin. In turn, component (b-1) is made up of (b-1-1) ahigh-melting crystalline polymer segment and (b-1-2) a low-meltingpolymer segment.

The high-melting crystalline polymer segment (b-1-1) within thepolyester block copolymer serving as component (b-1) is a polyesterformed from one or more compound selected from the group consisting ofaromatic dicarboxylic acids and ester-forming derivatives thereof anddiols and ester-forming derivatives thereof.

Illustrative examples of the aromatic dicarboxylic acids includeterephthalic acid, isophthalic acid, phthalic acid,2,6-naphthalenedicarboxylic acid, 2,7-naphthalenedicarboxylic acid,anthracenedicarboxylic acid, diphenyl-4,4′-dicarboxylic acid,diphenoxyethanedicarboxylic acid, 4,4′-diphenyletherdicarboxylic acid,5-sulfoisophthalic acid and sodium 3-sulfoisophthalate. In thisinvention, an aromatic dicarboxylic acid is primarily used. However,where necessary, some of this aromatic dicarboxylic acid may be replacedwith an alicyclic dicarboxylic acid such as 1,4-cyclohexanedicarboxylicacid, cyclopentanedicarboxylic acid or 4,4′-dicyclohexyldicarboxylicacid or with an aliphatic dicarboxylic acid such as adipic acid,succinic acid, oxalic acid, sebacic acid, dodecanedioic acid or a dimeracid. Exemplary ester-forming derivatives of dicarboxylic acids includelower alkyl esters, aryl esters, carboxylic acid esters and acid halidesof the above dicarboxylic acids.

Next, a diol having a molecular weight of 400 or less may be suitablyused as the diol. Specific examples include aliphatic diols such as1,4-butanediol, ethylene glycol, trimethylene glycol, pentamethyleneglycol, hexamethylene glycol, neopentyl glycol and decamethylene glycol;alicyclic diols such as 1,1-cyclohexanedimethanol,1,4-dicyclohexanedimethanol and tricyclodecanedimethanol; and aromaticdiols such as xylylene glycol, bis(p-hydroxy)diphenyl,bis(p-hydroxy)diphenylpropane,2,2′-bis[4-(2-hydroxyethoxy)phenyl]propane,bis[4-(2-hydroxyethoxy)phenyl]sulfone,1,1-bis[4-(2-hydroxyethoxy)phenyl]cyclohexane,4,4′-dihydroxy-p-terphenyl and 4,4′-dihydroxy-p-quaterphenyl. Exemplaryester-forming derivatives of diols include acetylated forms and alkalimetal salts of the above diols.

These aromatic dicarboxylic acids, diols and derivatives thereof may beused singly or two or more may be used together.

In particular, the following may be suitably used as component (b-1-1):high-melting crystalline polymer segments composed of polybutyleneterephthalate units derived from terephthalic acid and/or dimethylterephthalate together with 1,4-butanediol; high-melting crystallinepolymer segments composed of polybutylene terephthalate units derivedfrom isophthalic acid and/or dimethyl isophthalate together with1,4-butanediol; and copolymers of both.

The low-melting polymer segment serving as component (b-1-2) is analiphatic polyether and/or an aliphatic polyester.

Examples of the aliphatic polyether include poly(ethylene oxide) glycol,poly(propylene oxide) glycol, poly(tetramethylene oxide) glycol,poly(hexamethylene oxide) glycol, copolymers of ethylene oxide andpropylene oxide, ethylene oxide addition polymers of poly(propyleneoxide) glycol, and copolymer glycols of ethylene oxide andtetrahydrofuran. Examples of aliphatic polyesters includepoly(s-caprolactone), polyenantholactone, polycaprolactone, polybutyleneadipate and polyethylene adipate. In this invention, from the standpointof the elastic properties, suitable use can be made ofpoly(tetramethylene oxide) glycol, ethylene oxide adducts ofpoly(propylene oxide) glycol, copolymer glycols of ethylene oxide andtetrahydrofuran, poly(ε-caprolactone), polybutylene adipate andpolyethylene adipate. Of these, the use of, in particular,poly(tetramethylene oxide) glycol, ethylene oxide adducts ofpoly(propylene oxide) glycol and copolymer glycols of ethylene oxide andtetrahydrofuran is recommended. The number-average molecular weight ofthese segments in the copolymerized state is preferably from about 300to about 6,000.

Component (b-1) can be produced by a known method. Specifically, use canbe made of, for example, the method of carrying out atransesterification reaction on a lower alcohol diester of adicarboxylic acid, an excess amount of a low-molecular-weight glycol anda low-melting polymer segment component in the presence of a catalystand polycondensing the resulting reaction product, or the method ofcarrying out an esterification reaction on a dicarboxylic acid, anexcess amount of glycol and a low-melting polymer segment component inthe presence of a catalyst and polycondensing the resulting reactionproduct.

The proportion of component (b-1) accounted for by component (b-1-2) isfrom 30 to 60 wt %. The preferred lower limit in this case can be set to35 wt % or more, and the preferred upper limit can be set to 55 wt % orless. When the proportion of component (b-1-2) is too low, the impactresistance (especially at low temperatures) and the compatibility may beinadequate. On the other hand, when the proportion of component (b-1-2)is too high, the rigidity of the resin composition (and the molded body)may be inadequate.

The rigid resin serving as component (b-2) is not particularly limited.For example, one or more selected from the group consisting ofpolycarbonates, acrylic resins, styrene resins such as ABS resins andpolystyrenes, polyester resins, polyamide resins, polyvinyl chloridesand modified polyphenylene ethers may be used. In this invention, fromthe standpoint of compatibility, a polyester resin may be suitably used.More preferably, the use of polybutylene terephthalate and/orpolybutylene naphthalate is recommended.

Component (b-1) and component (b-2) are blended in a ratio, expressed as(b-1):(b-2), which is not particularly limited, although this ratio byweight is preferably set to from 50:50 to 90:10, and more preferablyfrom 55:45 to 80:20. When the proportion of component (b-1) is too low,the low-temperature impact resistance may be inadequate. On the otherhand, when the proportion of (b-1) is too high, the rigidity of thecomposition (and the molded body), as well as the moldingprocessability, may be inadequate.

A commercial product may be used as the polyester elastomer (B).Specific examples include those available as Hytrel® from DuPont-TorayCo. Ltd.

Component (B) has a material hardness on the Shore D hardness scalewhich, to enhance the spin rate on approach shots, is preferably 35 orless, more preferably 33 or less, and even more preferably 31 or less.The lower limit is a Shore D hardness of preferably at least 27, andmore preferably at least 29.

Component (B) has a rebound resilience which, to enhance the spin rateon approach shots, is preferably at least 65%, more preferably at least67%, and even more preferably at least 69%. The rebound resilience ismeasured according to JIS-K 6255: 2013.

Component (B) has a melt viscosity which is preferably from 0.2×10⁴dPa·s to 1.0×10⁴ dPa·s. With this melt viscosity, hardenability aftermolding of the resin composition is imparted and a decrease inmoldability (productivity) can be suppressed. This melt viscosityindicates the value measured with a capillary viscometer at atemperature of 200° C. and a shear rate of 243 sec⁻¹ in accordance withISO 11443: 1995.

Component (B) is blended in a proportion which is not more than 45 wt %,preferably not more than 40 wt %, and more preferably not more than 30wt %, of the resin composition. At above this value, decreases in themoldability and the scuff resistance may occur.

The blending ratio (A)/(B) of component (A) and component (B) ispreferably from 90/10 to 60/40 by weight. When the content of component(B) is higher than this range, the moldability may worsen or the scuffresistance may decrease. On the other hand, when the component (B)content is lower than this range, an improvement in the spin rate onapproach shots may not be achieved.

The resin composition containing components (A) and (B) may includeother resin materials in addition to the above-described resincomponents. The purposes for doing so are, for example, to furtherimprove the flowability of the golf ball resin composition and toincrease such ball properties as the rebound and the scuff resistance.

Examples of other resin materials that may be used include polyesterelastomers, polyamide elastomers, ionomer resins,ethylene-ethylene/butylene-ethylene block copolymers and modified formsthereof, polyacetals, polyethylenes, nylon resins, methacrylic resins,polyvinyl chlorides, polycarbonates, polyphenylene ethers, polyarylates,polysulfones, polyethersulfones, polyetherimides and polyamideimides.These may be used singly or two or more may be used together.

In addition, an active isocyanate compound may be included in the aboveresin composition. This active isocyanate compound reacts with thepolyurethane or polyurea serving as the base resin, enabling the scuffresistance of the overall resin composition to be further increased.Moreover, the isocyanate has a plasticizing effect which increases theflowability of the resin composition, enabling the moldability to beimproved.

Any isocyanate compound employed in conventional polyurethanes may beused without particular limitation as the above isocyanate compound. Forexample, aromatic isocyanate compounds that may be used include2,4-toluene diisocyanate, 2,6-toluene diisocyanate and mixtures of both,4,4-diphenylmethane diisocyanate, m-phenylene diisocyanate and4,4′-biphenyl diisocyanate. Use can also be made of the hydrogenatedforms of these aromatic isocyanate compounds, such asdicyclohexylmethane diisocyanate. Other isocyanate compounds that may beused include aliphatic diisocyanates such as tetramethylenediisocyanate, hexamethylene diisocyanate (HDI) and octamethylenediisocyanate, and alicyclic diisocyanates such as xylene diisocyanate.Further examples of isocyanate compounds that may be used includeblocked isocyanate compounds obtained by reacting the isocyanate groupson a compound having two or more isocyanate groups on the ends with acompound having active hydrogens, and uretdiones obtained by thedimerization of isocyanate.

The amount of the above isocyanate compounds included per 100 parts byweight of the polyurethane or polyurea resin serving as component (A) ispreferably at least 0.1 part by weight, and more preferably at least 0.5part by weight. The upper limit is preferably not more than 30 parts byweight, and more preferably not more than 20 parts by weight. When toolittle is included, a sufficient crosslinking reaction may not beobtained and an increase in the properties may not be observable. On theother hand, when too much is included, discoloration over time due toheat and ultraviolet light may increase, or problems such as a loss ofthermoplasticity or a decline in resilience may arise.

In addition, optional additives may be suitably included in the aboveresin composition according to the intended use thereof. For example,when the resin composition is to be used as a golf ball cover material,various additives, such as inorganic fillers, organic staple fibers,reinforcing agents, crosslinking agents, pigments, dispersants,antioxidants, ultraviolet absorbers and light stabilizers, may be addedto the above ingredients. When such additives are included, the amountthereof per 100 parts by weight of the base resin is preferably at least0.1 part by weight, and more preferably at least 0.5 part by weight, butpreferably not more than 10 parts by weight, and more preferably notmore than 4 parts by weight.

In order to enhance the spin rate on approach shots, the reboundresilience of the resin composition, as measured in accordance withJIS-K 6255: 2013, must be at least 60%, and is preferably at least 62%,and more preferably at least 64%. The upper limit must be not more than72%, and is preferably not more than 70% and more preferably not morethan 68%.

The resin composition has a material hardness on the Shore D hardnessscale which, to enhance the spin rate on approach shots, must be 42 orless, and is preferably 41 or less, and more preferably 40 or less. Fromthe standpoint of moldability, the lower limit in the Shore D hardnessis preferably at least 30, and more preferably at least 35.

The resin composition may be prepared by mixing together the ingredientsusing any of various types of mixers, such as a kneading-typesingle-screw or twin-screw extruder, a Banbury mixer, a kneader or aLabo Plastomill. Alternatively, the ingredients may be mixed together bydry blending when the resin composition is injection-molded. Inaddition, in cases where an active isocyanate compound is used, it maybe incorporated at the time of resin mixture using various types ofmixers, or a resin masterbatch already containing the active isocyanatecompound and other ingredients may be separately prepared and thevarious components mixed together by dry blending when the resincomposition is injection-molded.

The method of molding the cover from the above resin composition mayinvolve, for example, feeding the resin composition into an injectionmolding machine and molding the cover by injecting the molten resincomposition over the ball core. In this case, the molding temperaturediffers according to the type of polyurethane or polyurea (A) serving asthe base resin, but is typically in the range of 150 to 270° C.

The cover has a thickness of preferably at least 0.4 mm, more preferablyat least 0.5 mm, and even more preferably at least 0.6 mm. The upperlimit is preferably not more than 3.0 mm, and more preferably not morethan 2.0 mm.

When at least one intermediate layer is interposed between the abovecore and cover, various types of thermoplastic resins used as golf ballcover materials, particularly ionomer resins, may be suitably employedas the intermediate layer material. A commercial product may be used asthe ionomer resin. In such a case, the thickness of the intermediatelayer may be set within a similar range as the cover thickness.

Numerous dimples are provided on the surface of the outermost layer ofthe inventive golf ball for reasons having to do with the aerodynamicperformance. The number of dimples formed on the surface of theoutermost layer is not particularly limited. However, to enhance theaerodynamic performance and increase the distance traveled by the ball,this number is preferably at least 250, more preferably at least 270,even more preferably at least 290, and most preferably at least 300. Theupper limit is preferably not more than 400, more preferably not morethan 380, and even more preferably not more than 360.

In this invention, a coating layer is formed on the cover surface. Atwo-part curable urethane coating may be suitably used as the coatingthat forms this coating layer. Specifically, in this case, the two-partcurable urethane coating is one that includes a base resin composedprimarily of a polyol resin and a curing agent composed primarily of apolyisocyanate.

A known method may be used without particular limitation as the methodfor applying this coating onto the cover surface and forming a coatinglayer. Use can be made of a desired method such as air gun painting orelectrostatic painting.

The thickness of the coating layer, although not particularly limited,is typically from 8 to 22 μm, and preferably from 10 to 20 μm.

The golf ball of the invention can be made to conform to the Rules ofGolf for play. The inventive ball may be formed to a diameter which issuch that the ball does not pass through a ring having an inner diameterof 42.672 mm and is not more than 42.80 mm, and to a weight which ispreferably between 45.0 and 45.93 g.

The following Examples and Comparative Examples are provided toillustrate the invention, and are not intended to limit the scopethereof.

Examples 1 to 6, Comparative Examples 1 to 6

In Examples 1, 3 and 5 according to the invention and ComparativeExamples 1, 2 and 5, a core-forming rubber composition formulated asshown in Table 1 and common to all of the Examples was prepared and thenmolded and vulcanized to produce a 38.6 mm diameter core. In Examples 2,4 and 6 according to the invention and Comparative Examples 3, 4 and 6,the golf ball core is produced in the same way as in the foregoingExamples and Comparative Examples.

TABLE 1 Rubber composition parts by weight cis-1,4-Polybutadiene 100Zinc acrylate 27 Zinc oxide 4.0 Barium sulfate 16.5 Antioxidant 0.2Organic peroxide (1) 0.6 Organic peroxide (2) 1.2 Zinc salt ofpentachlorothiophenol 0.3 Zinc stearate 1.0

Details on the above core materials are given below.

-   cis-1,4-Polybutadiene: Available under the trade name “BR 01” from    JSR Corporation-   Zinc acrylate: Available from Nippon Shokubai Co., Ltd.-   Zinc oxide: Available from Sakai Chemical Co., Ltd.-   Barium sulfate: Available from Sakai Chemical Co., Ltd.-   Antioxidant: Available under the trade name “Nocrac NS6” from Ouchi    Shinko Chemical Industry Co., Ltd.-   Organic peroxide (1): Dicumyl peroxide, available under the trade    name “Percumyl D” from NOF Corporation-   Organic peroxide (2): A mixture of    1,1-di(tert-butylperoxy)cyclohexane and silica, available under the    trade name “Perhexa C-40” from NOF Corporation-   Zinc stearate: Available from NOF Corporation

Next, in Examples 1, 3 and 5 and Comparative Examples 1, 2 and 5, anintermediate layer-forming resin material was injection-molded over the38.6 mm diameter core, thereby producing an intermediate layer-encasedsphere having a 1.25 mm thick intermediate layer. In Examples 2, 4 and 6and Comparative Examples 3, 4 and 6, an intermediate layer-encasedsphere having an intermediate layer is produced in the same way as inthe foregoing Examples and Comparative Examples. This intermediatelayer-forming resin material, which is a resin blend common to all ofthe Examples, is composed of 50 parts by weight of the sodiumneutralization product of an ethylene-unsaturated carboxylic acidcopolymer having an acid content of 18 wt % and 50 parts by weight ofthe zinc neutralization product of an ethylene-unsaturated carboxylicacid copolymer having an acid content of 15 wt %, for a total of 100parts by weight.

In Examples 1, 3 and 5 and Comparative Examples 1, 2 and 5, theoutermost layer-forming cover material shown in Table 2 below was theninjection-molded over the above intermediate layer-encased sphere,thereby producing a 42.7 mm diameter three-piece golf ball having a 0.8mm thick outermost layer. At this time, dimples common to all of theExamples and Comparative Examples were formed on the surface of thecover. With regard to the cover-forming resin composition, theingredients were mixed by blending in the amounts shown in Table 2, andthe resulting composition was injection-molded at a molding temperatureof between 200° C. and 250° C.

In Examples 2, 4 and 6 and Comparative Examples 3, 4 and 6, three-piecegolf balls are produced in the same way as in the foregoing Examples andComparative Examples.

Details on the ingredients included in the compositions in Tables 2 aregiven below.

-   TPU (1): An ether-type thermoplastic polyurethane available from DIC    Covestro Polymer. Ltd. under the trade name “Pandex” (Shore D    hardness, 43; rebound resilience, 61%)-   TPU (2): An ether-type thermoplastic polyurethane available from DIC    Covestro Polymer, Ltd. under the trade name “Pandex” (Shore D    hardness, 47; rebound resilience, 54%)-   TPU (3): An ether-type thermoplastic polyurethane available from DIC    Covestro Polymer, Ltd. under the trade name “Pandex” (Shore D    hardness, 35; rebound resilience, 64%)-   Polyester Elastomer 1: A thermoplastic polyether-ester elastomer    available from DuPont-Toray Co., Ltd. under the trade name “Hytrel    3001” (Shore D hardness, 31; rebound resilience, 79%)-   Polyester Elastomer 2: A thermoplastic polyether-ester elastomer    available from DuPont-Toray Co., Ltd. under the trade name “Hytrel    4001” (Shore D hardness, 37: rebound resilience, 77%)-   Plasticizer: Methyl oleate

Properties of Resin Composition (1) Rebound Resilience:

The rebound resiliences of the resin compositions measured in accordancewith JIS-K 6255: 2013 are shown in Table 2.

(2) Melt Viscosity:

The melt viscosities measured with a capillary viscometer at atemperature of 200° C. and a shear rate of 243 sec⁻¹ in accordance withISO 11443: 1995 are shown in Table 2.

The spin performance on approach shots, scuff resistance, feel at impactand moldability of each of the golf balls are evaluated by the followingmethods. The results are shown in Table 2.

Spin Performance on Approach Shots

A sand wedge (SW) is mounted on a golf swing robot and the backspin rateof the ball immediately after being struck at a head speed (HS) of 20m/s is measured with an apparatus for measuring the initial conditions.

Scuff Resistance

The golf balls are held isothermally at 23° C. and five balls of eachtype are hit at a head speed of 33 m/s using as the club a pitchingwedge (PW) mounted on a swing robot machine. The damage to the ball fromthe impact is visually rated according to the following criteria.

Excellent (Exc): Slight scuffing or substantially no apparent scuffing.

Good: Slight fraying of surface or slight dimple damage.

NG: Dimples completely obliterated in places.

Feel at Impact

Sensory evaluations of the feel of the ball when struck with a sandwedge (SW) are carried out by ten skilled amateur golfers on approachshots at 30 to 40 yards, and the feel is rated according to thefollowing criteria.

Rating Criteria:

-   -   Good: Six or more of the ten golfers rate the feel as good    -   Fair: Four or five of the ten golfers rate the feel as good    -   NG: Three or fewer of the ten golfers rate the feel as good

Moldability (Mold Releasability)

Releasability of the ball from the mold following injection molding ofthe cover is rated according to the following criteria for the balls ineach Example.

-   -   Good: External defects such as runner stubs and ejector pin        marks do not arise during demolding.    -   Fair: External defects such as runner stubs and ejector pin        marks arise during demolding, but molding proceeds without        difficulty.    -   NG: External defects such as runner stubs and ejector pin marks        arise during demolding, and molding is impossible.

TABLE 2 Example 1 2 3 4 5 6 Cover (A) TPU (1) 100 100 100 100 100 100Composition (A) TPU (2) (pbw) (A) TPU (3) (B) Polyester elastomer 1 5 1015 20 30 40 (B) Polyester elastomer 2 Plasticizer Properties Meltviscosity of (B) 0.348 0.348 0.348 0.348 0.348 0.348 (×10⁴ dPa · s)Resin Composition Hardness (Shore D) 42 42 42 41 40 38 Reboundresilience (%) 62 62 63 64 67 70 Evaluation results Spin rate onapproach shots (rpm) 6,457 6,488 6,526 6,548 6,609 6,664 Scuffresistance good good good good good good Feel at impact good good goodgood good good Moldability good good good good good good ComparativeExample 1 2 3 4 5 6 Cover (A) TPU (1) 100 100 100 100 Composition (A)TPU (2) 100 (pbw) (A) TPU (3) 100 (B) Polyester elastomer 1 50 10 (B)Polyester elastomer 2 15 Plasticizer 5 Properties Melt viscosity of (B)— 0.285 0.348 0.348 — — (×10⁴ dPa · s) Resin Composition Hardness (ShoreD) 43 43 35 47 42 35 Rebound resilience (%) 61 61 74 56 61 64 Evaluationresults Spin rate on approach shots (rpm) 6,384 6,367 6,730 6,146 6,3706,608 Scuff resistance good good NG NG gooc good Feel at impact fairfair good NG fair good Moldability good good NG good good NG

As demonstrated by the results in Table 2, the golf balls of ComparativeExamples 1 to 6 are inferior in the following respects to the golf ballsobtained in Examples 1 to 6 according to the present invention.

In Comparative Example 1, the hardness of the resin composition ishigher than the prescribed range, as a result of which the spin rate onapproach shots is inadequate.

In Comparative Example 2, the hardness of the resin composition ishigher than the prescribed range, as a result of which the spin rate onapproach shots is inadequate.

In Comparative Example 3, the blending ratio of component (B) includedin the resin composition is high, as a result of which a good scuffresistance and moldability are not obtained.

In Comparative Example 4, the hardness of the resin composition ishigher than the prescribed range, as a result of which the spin rate onapproach shots is inadequate.

In Comparative Example 5, the rebound resilience of the resincomposition is lower than the prescribed range, as a result of which thespin rate on approach shots is inadequate.

In Comparative Example 6, component (B) is not included in the resincomposition. As a result, although the spin rate is satisfactory, thehardenability is low and the moldability is inadequate.

Japanese Patent Application No. 2020-096539 is incorporated herein byreference.

Although some preferred embodiments have been described, manymodifications and variations may be made thereto in light of the aboveteachings. It is therefore to be understood that the invention may bepracticed otherwise than as specifically described without departingfrom the scope of the appended claims.

1. A golf ball comprising a rubber core of at least one layer and acover of at least one layer encasing the core, wherein at least onelayer of the cover is formed of a resin composition comprised of (A)polyurethane or polyurea, and (B) a thermoplastic polyester elastomer,component (B) being included in a ratio of not more than 45 wt % of theoverall amount of the resin composition and the resin composition havinga Shore D hardness of 42 or less and a rebound resilience of from 60 to72%.
 2. The golf ball of claim 1, wherein the rebound resilience of theresin composition is from 62 to 70%.
 3. The golf ball of claim 1,wherein the polyurethane or polyurea serving as component (A) has aShore D hardness of 45 or less and a rebound resilience of at least 55%.4. The golf ball of claim 1, wherein the thermoplastic polyesterelastomer serving as component (B) has a Shore D hardness of not morethan 35 and a rebound resilience of at least 65%.
 5. The golf ball ofclaim 1, wherein component (B) has a melt viscosity at 200° C. and ashear rate of 243 sec⁻¹ which is from 0.2×10⁴ to 1.0×10⁴ dPa·s.